Virtually every electronic device includes one or more varieties of printed circuit boards (“PCBs”) (also referred to as printed wiring boards or “PWBs”). PCBs are relatively thin, layered substrates upon which integrated circuits and other electronic components are mounted. A printed circuit board typically includes a plurality of electrically conductive and insulating layers arranged in a sandwich-like fashion. Conductive layers generally have conductive paths or traces, which are chemically or mechanically etched out of the bulk conductive layer, thus isolated from one another by insulating material and routed within a plane. These traces are generally designed to electrically contact conductive portions of the electronic components mounted on the PCB, forming electrical interconnects. Insulating layers electrically isolate conductive layers from one another. The principle structure of conductive traces and layers of insulating material is also used on a smaller scale within a packaged microchip having a PCB-like package substrate.
The insulating layers typically are made of preimpregnated (prepreg) materials such as FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), and FR-4 (Woven glass and epoxy). FR-4 is the material of choice in the building of PCBs used in high-end industrial, consumer, and military electronic equipment due to its ability to absorb less moisture, its strength and stiffness, and its flame resistance. Numerous variations of FR-4 are available on the market, such as FR-408 and Polyclad 370HR. FR-408 has a lower dissipation factor at high frequencies than many other materials making it desirable for use in PCBs requiring the use of high speed signals. However, FR-408 and other insulating materials that have low dissipation factors at high frequencies have higher costs. It would be desirable to manufacture a PCB at lower cost while maintaining the capabilities of materials such as FR-408.